1. Field of the Invention
This invention relates to an image-forming apparatus employing an electrophotographic recording system having an exposure unit which radiates light modulated in accordance with image signals and a contact developing unit for developing electrostatic latent images formed by this exposure unit. More particularly, this invention relates to an image-forming apparatus which can prevent mismatching in the expression of density gradation and spots around line images from being caused by the shortage of charge quantity due to reversely charged toner. This invention also relates to a process cartridge used in the image-forming apparatus.
2. Related Background Art
In general, image-forming apparatus employing an electrophotographic recording system have a photosensitive member which is rotatively driven, a charging assembly which electrostatically charges the surface of the photosensitive member uniformly, an exposure means by which the surface of the photosensitive member is exposed to form an electrostatic latent image corresponding to image signals, a developing means by which the electrostatic latent image is developed with a toner to form a visible image, a transfer means by which the visible image is transferred onto recording paper, and a fixing means by which the visible image transferred onto the recording paper is fixed.
In this case, as the developing means, two types are known in which a developing roller comes into contact with the photosensitive member to perform development (hereinafter called a contact developing system) and the developing roller performs development in a state of noncontact with the photosensitive member (hereinafter called a noncontact developing system). The contact developing system includes a type in which, as disclosed in Japanese Patent Applications Laid-Open No. 62-223711 and No. 1-239566, the developing roller is elastically brought into contact with the surface of the photosensitive member and a type in which, as disclosed in Japanese Patent Applications Laid-Open No. 4-247478, as the developing roller a roller comprised of an elastic member is provided with a resin thin-sheet sleeve on its surface.
FIG. 4 is a diagrammatic cross-sectional view showing the construction of an example of a known image-forming apparatus employing as the developing means the contact developing system (hereinafter this apparatus is called a conventional apparatus).
In FIG. 4, reference numeral 101 denotes a drum-shaped photosensitive member (photosensitive drum); 102, a contact developing roller; 103, a developing unit; 104, a transfer roller; 105, a charging roller; 106, an exposure means; 108, a toner feed roller; 109, a developing blade; and 110, a toner.
The photosensitive drum 101 is constituted of a drum-shaped metallic crude pipe and a photosensitive material applied to its surface. When operated, it is rotatively driven around a rotating shaft in the direction of an arrow shown in the drawing, by means of a drive unit (not shown). The developing roller 102 and the developing unit 103 constitute the developing means. The developing roller 102 is so constructed and disposed as to be always in contact with the surface of the photosensitive drum 101 and rotatable with the rotation of the photosensitive drum 101. The developing unit 103 has a developing blade 109 so constructed as to come into touch with the developing roller 102. The toner 110 is made to pass the part of the developing blade 109 touching the developing roller 102, and the quantity of the toner 110 carried on the developing roller 102 is regulated to form a thin layer of the toner 110 on the developing roller 102. At the same time, the friction caused at the touching part imparts a sufficient triboelectric charges (triboelectricity) to the toner 110. Also, in the developing unit 103, the toner feed roller 108, coming into contact with the developing roller 102, is provided at a position which is on the upstream side of the developing blade 109 in the direction of the rotation of the developing roller 102, to feed the toner 110 to the developing roller 102 so as to be carried thereon.
The transfer roller 104 constitutes the transfer means, and is so constructed that it is rotated in contact with the photosensitive drum 101 and the recording paper (not shown) passes the contact zone formed between the photosensitive drum 101 and the transfer roller 104 at the time of transfer.
The charging roller 105 electrostatically charges the surface of the photosensitive drum 101 uniformly at a constant potential by means of a charge voltage generation power source (not shown). It is kept in pressure contact with the surface of the photosensitive drum 101 at a stated pressure to electrostatically charges the surface of the photosensitive drum 101 while being rotated with the rotation of the photosensitive drum 101.
The exposure means 106 feeds light signals modulated in accordance with image signals sent from an image signal source (not shown). It provides the surface of the photosensitive drum 101 with the light signals to form thereon an electrostatic latent image corresponding to the image signals.
How the conventional apparatus is operated is described below. To describe the whole operation of the conventional apparatus, the photosensitive drum 101 rotated in the direction of an arrow a shown in FIG. 4 is first uniformly charged on its surface by means of the charging roller 105, and then an electrostatic latent image corresponding to image signals is formed on its surface by means of the exposure means 106. Subsequently, the electrostatic latent image is developed by making the toner 110 adhere thereto by means of the developing roller 102 to which development voltage has been applied from the charge voltage generation power source (not shown), so that a visible image corresponding to this electrostatic latent image is formed on the surface of the photosensitive drum 101. This visible image formed on the surface of the photosensitive drum 101 is transferred onto the recording paper by means of the transfer roller 104. The visible image thus transferred is fixed onto the recording paper and thereafter taken out as a recorded image together with the recording paper. Meanwhile, the surface part of the photosensitive drum 101 having passed the part of the transfer roller 104 is cleaned to remove the toner through a cleaning means (not shown). Then, the process described above is again carried out repeatedly.
The construction of a photosensitive layer of the photosensitive drum 101 is roughly grouped into a single layer type containing both a charge-generating material and a charge-transporting material in the same layer and a multilayer type having a charge generation layer containing a charge-generating material and a charge transport layer containing a charge-transporting material.
An electrophotographic photosensitive member having the photosensitive layer of a multilayer type includes a photosensitive member comprising a substrate and superposed thereon the charge generation layer and the charge transport layer in this order. The charge transport layer is formed by applying a solution prepared by dissolving in a resin having film-forming properties a charge-transporting material including polycyclic aromatic compounds having a structure such as a biphenylene, anthracene, pyrene or phenanthrene structure in the main chain or side chain; nitrogen-containing ring compounds such as indole, carbazole, oxazole and pyrazoline; hydrazone compounds and styryl compounds; followed by drying. The resin having film-forming properties may include polyester, polycarbonate, polystyrene, polymethacrylate and polyarylate. The charge generation layer is formed by coating the substrate with a dispersion prepared by dispersing in a resin such as polyvinyl butyral, polystyrene, polyvinyl acetate or acrylic resin a charge-generating material including azo pigments such as Sudan Red and Diamond Blue, quinone pigments such as pyrene, quinone and anthanthrone, quinocyanine pigments, perylene pigments, indigo pigments such as indigo and thioindigo, and phthalocyanine pigments, followed by drying, or by vacuum depositing any of the above pigments on the substrate.
As for the photosensitive layer of a single-layer type, it is formed by coating the substrate with a solution prepared by dispersing or dissolving the above charge-generating material and charge-transporting material, followed by drying.
As a method of expressing density gradation in electrophotographic image-forming apparatus, widely known are a gradation expression in which light is radiated from a light source on an original and the latent-image potential on a photosensitive drum is made variable in accordance with the quantity of light reflecting therefrom (an electrostatic latent image thus formed is hereinafter called an analogue latent image), and a gradation expression in which a photosensitive drum is exposed to light modulated in accordance with image signals, emitted from an exposure unit, and its exposure area is made variable (an electrostatic latent image thus formed is hereinafter called a digital latent image). Where the contact developing system is used to develop these electrostatic latent images, density gradation characteristics may greatly deviate depending on the quantity of triboelectricity of a toner.
FIG. 5 shows density gradation characteristics with respect to analogue latent images where the quantity of triboelectricity of a toner differs. In FIG. 5, a curve shown by solid-black plot marks indicates a case in which the toner has proper quantity of triboelectricity; and a curve shown by solid-white plot marks, a case in which the toner has decreased in quantity of triboelectricity. As shown in FIG. 5, where the toner has decreased in quantity of triboelectricity, the density (image density) rises abruptly from a low contrast potential and the density becomes kept saturated even when the contrast potential is made higher. On the other hand, where the toner has a proper quantity of triboelectricity, density gradation characteristics are obtained in accord with the contrast potential. This is a phenomenon caused by a difference in mirror image force on the developing roller due to a difference in toner""s triboelectricity. It is presumed that the toner decreased in the quantity of triboelectricity has so weak a mirror image force to the developing roller as to become subject to the force given from an electric field formed between the photosensitive drum and the developing roller, so that the toner tends to move easily to the photosensitive drum even at a low contrast potential. The toner""s triboelectricity may considerably vary depending on how long the toner is used and how many times it is used. Thus, it can be said that the density gradation characteristics in the contact developing system come out against the analogue latent images.
Then, FIG. 6 shows density gradation characteristics with respect to digital latent images where the quantity of triboelectricity of a toner differs. In FIG. 6, a curve shown by solid-black plot marks indicates a case in which the toner has a proper quantity of triboelectricity; a curve shown by solid-white plot marks, a case in which the toner has decreased in the quantity of triboelectricity; and a solid line, ideal density gradation characteristics. As shown in FIG. 6, compared with the density gradation characteristics concerning the analogue latent images, substantially good density gradation characteristics are obtained even where the toner has decreased in a quantity of triboelectricity, thus the digital latent images are preferable for the contact developing system. This difference in density gradation characteristics of digital latent images is a difference in density of electrostatic latent images formed at the high contrast potentials shown in FIG. 5. It is presumed that the density is substantially equally outputted in either of the toner with a low quantity of triboelectricity and the toner with a proper quantity of triboelectricity, and hence, compared with the case of analogue latent images, the difference in the density gradation characteristics due to the difference in the quantity of triboelectricity is less in the case of digital latent images.
However, as shown in FIG. 6, where the toner has a low quantity of triboelectricity, the density gradation characteristics shift at a higher density than the ideal density gradation characteristics even at a light gradation. Hence, in the formation of images like photographic images, too dense images may be formed as a whole, and the images may look dark and dull. The same applies also to a case in which line images as typified by characters or letters are formed. When the toner has a low quantity of triboelectricity, the toner may move in excess to line-image latent images to cause an increase in height of toner images on the photosensitive drum, resulting in an increase in toner consumption and causing a faulty image called toner spots around line images.
Accordingly, in the contact developing system, in order to maintain good density gradation characteristics and prevent the toner consumption from increasing, the quantity of triboelectricity must be kept from lowering.
In the contact developing system, however, the toner is regulated by the developing blade to have a prescribed toner layer thickness and at the same time provided with a stated quantity of triboelectricity. When the surface of the photosensitive drum (an image-bearing member which holds thereon the electrostatic latent image) is rubbed with the toner, the quantity of triboelectricity may become lower than a prescribed value or a toner charged to a reverse polarity may be formed, if the relation of triboelectric series of the photosensitive drum surface layer with respect to the toner is the same polarity as that of the toner. Then, the lowering of the quantity of triboelectricity of the toner is accelerated because the number of times of its friction with the photosensitive drum increases with times the developing unit as used. As the result, even though the toner has a proper quantity of triboelectricity at the initial stage, it becomes a toner having a low quantity of triboelectricity to cause problems such as crushed line images, spots around line images and an increase in toner consumption. Moreover, the toner charged in a reverse polarity may adhere to nonimage areas on the photosensitive drum to appear as reversal fog, also causing such a problem that the toner consumption increases.
An object of the present invention is to provide an image-forming apparatus having solved the above problems. That is, an object of the present invention is to provide an image-forming apparatus which can prevent the toner""s quantity of triboelectricity from lowering in the contact developing system, and can well maintain the density gradation characteristics to form images (visible toner images) stably in the step of developing electrostatic latent images formed by exposing a photosensitive drum to light modulated in accordance with image signals which is emitted from an exposure unit while varying its exposure area.
Another object of the present invention is to provide an image-forming apparatus which can prevent any excess toner consumption.
Still another object of the present invention is to provide an image-forming apparatus which can be free of any reversal fog even in its long-term continuous service.
The present invention provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
a charging means for charging the surface of the image-bearing member electrostatically;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means; and
a developing unit which has at least a toner-carrying member for carrying and transporting a toner thereon; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein, in the triboelectric series relationship between the toner and a surface layer of the image-bearing member, the surface layer of the image-bearing member has a charge polarity which is a different polarity with respect to the charge polarity of the toner in the developing unit.
The present invention also provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
a charging means for charging the surface of the image-bearing member electrostatically;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means; and
a plurality of developing units for developing electrostatic latent images with toners having different colors;
wherein;
the developing units each have at least a toner-carrying member for carrying and transporting thereon a toner having different color; the toner-carrying member of one developing unit selected from the developing units being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible; these steps being sequentially repeated for each of the remaining developing units to form toner images; and
in the triboelectric series relationship between each toner and a surface layer of the image-bearing member, the surface layer of the image-bearing member has a charge polarity which is a different polarity with respect to the charge polarity of each toner in the developing unit.
The present invention still also provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, followed by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting a toner thereon; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
in the triboelectric series relationship between the toner and a surface layer of the image-bearing member, the surface layer of the image-bearing member having a charge polarity which is a different polarity with respect to the charge polarity of the toner in the developing unit.
The present invention further provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing the image-bearing member to light; and
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a negatively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive is in the order of the external additive, the toner particles and the surface layer of the image-bearing member from the negative side.
The present invention still further provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing the image-bearing member to light; and
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a negatively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive is in the order of the toner particles, the external additive and the surface layer of the image-bearing member from the negative side.
The present invention still further provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing the image-bearing member to light; and
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a negatively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive is in the order of the toner particles, the surface layer of the image-bearing member and the external additive from the negative side.
The present invention still further provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing the image-bearing member to light; and
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a positively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive is in the order of the external additive, the toner particles and the surface layer of the image-bearing member from the positive side.
The present invention still further provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing the image-bearing member to light; and
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a positively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive is in the order of the toner particles, the external additive and the surface layer of the image-bearing member from the positive side.
The present invention still further provides an image-forming apparatus comprising:
an image-bearing member for holding thereon an electrostatic latent image;
an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing the image-bearing member to light; and
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a positively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image;
wherein the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive is in the order of the toner particles, the surface layer of the image-bearing member and the external additive from the positive side.
The present invention still further provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, followed by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a negatively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive being in the order of the external additive, the toner particles and the surface layer of the image-bearing member from the negative side.
The present invention still further provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, followed by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a negatively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive being in the order of the toner particles, the external additive and the surface layer of the image-bearing member from the negative side.
The present invention still further provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, followed by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a negatively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive being in the order of the toner particles, the surface layer of the image-bearing member and the external additive from the negative side.
The present invention still further provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, followed by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a positively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive being in the order of the external additive, the toner particles and the surface layer of the image-bearing member from the positive side.
The present invention still further provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, following by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a positively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive being in the order of the toner particles, the external additive and the surface layer of the image-bearing member from the positive side.
The present invention still further provides a process cartridge which is detachably mountable to the main body of an image-forming apparatus for forming a fixed image by developing with a toner an electrostatic latent image formed on an image-bearing member to form a toner image, and transferring the toner image to a transfer medium either via an intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member, followed by fixing; the process cartridge comprising:
the image-bearing member for holding thereon the electrostatic latent image;
a developing unit which has at least a toner-carrying member for carrying and transporting thereon a positively chargeable toner having toner particles and at least one external additive; the toner-carrying member being brought into contact with the image-bearing member to form a developing zone, and in the developing zone the toner being made to adhere electrically to the electrostatic latent image formed on the image-bearing member, to render the electrostatic latent image visible to form a toner image; and
none or at least one of means selected from the group consisting of:
(a) a charging means for charging the surface of the image-bearing member electrostatically;
(b) an exposure unit for forming the electrostatic latent image on the image-bearing member by exposing to light the image-bearing member having been charged by the charging means;
(c) a transfer means for transferring the toner image formed by the developing unit, to the transfer medium either via the intermediate transfer member or directly transferring the toner image to a transfer member without using an intermediate transfer member; and
(d) a cleaning means for removing a toner remaining on the image-bearing member after the toner image has been transferred to the transfer medium; and being supported integrally together with the image-bearing member and the developing unit;
the triboelectric series relationship between a surface layer of the image-bearing member, the toner particles and the external additive being in the order of the toner particles, the surface layer of the image-bearing member and the external additive from the positive side.